Adult obesity diagnostic tool: A narrative review

Obesity is a complex chronic metabolic disorder characterized by abnormalities in lipid metabolism. Obesity is not only associated with various chronic diseases but also has negative effects on physiological functions such as the cardiovascular, endocrine and immune systems. As a global health problem, the incidence and prevalence of obesity have increased significantly in recent years. Therefore, understanding assessment methods and measurement indicators for obesity is critical for early screening and effective disease control. Current methods for measuring obesity in adult include density calculation, anthropometric measurements, bioelectrical impedance analysis, dual-energy X-ray absorptiometry, computerized imaging, etc. Measurement indicators mainly include weight, hip circumference, waist circumference, neck circumference, skinfold thickness, etc. This paper provides a comprehensive review of the literature to date, summarizes and analyzes various assessment methods and measurement indicators for adult obesity, and provides insights and guidance for the innovation of obesity assessment indicators.


Introduction
Obesity refers to a state of disordered energy metabolism in the body caused by complex interactions between genetic and environmental factors.Prolonged periods of being in a relatively obese state not only affect an individual's health and quality of life, but also lead to adverse changes in the structure and function of various body systems.It can even pose potential risks to an individual's psychological well-being, resulting in negative effects such as anxiety, low self-esteem, depression, and more. [1]ccording to the World Obesity Federation, [2] By 2020, the global number of overweight or obese people will be approximately 2603 million, with a prevalence rate of 38%.In addition, the global number of obese people will be approximately 988 million, with an obesity rate of 14%.It is projected that by 2035, more than 4 billion people worldwide will be overweight or obese, representing more than half of the world's population.Obesity not only affects the quality of life and life expectancy of individuals, but also places a significant economic burden on global healthcare systems. [3]It is therefore essential to fully understand the diagnostic criteria and assessment indicators for obesity in order to provide support and new strategies for early intervention or prevention.
The body mass index (BMI) formula, originally proposed by Quetelet, was once considered an effective tool for screening for obesity.Due to its convenience, safety and low cost, this screening method was widely accepted and applied by the general public. [4]However, after long-term large-scale application, it was found that this obesity screening tool has limited accuracy and is not applicable to all ethnic groups.Inaccurate and inaccurate diagnoses have a significant impact on the healthcare system.As a result, researchers have continuously explored new ways to diagnose obesity. [5]Despite the may limitations of using BMI to diagnose obesity, it is undeniable that this indicator remains highly effective as a crude screening tool for large sample sizes.Long-term application of research suggests that the higher an individual's BMI, the greater the need to perform additional assessments for potential metabolic abnormalities and complications. [6]Despite the many limitations in using BMI for diagnosing obesity, additional information is required in practical diagnosis, such as details about fat distribution, waist circumference, subcutaneous fat thickness, and the impact of fat accumulation on individuals.However, it is undeniable that this indicator remains highly effective as a rough screening tool for large sample sizes.Additionally, the higher the BMI value, the more necessary it is to conduct additional assessments for potential metabolic abnormalities and complications.Similar to BMI, there are numerous methods for assessing obesity, but they generally have many limitations.Therefore, in practical diagnosis, it is necessary to obtain additional information such as fat distribution, waist circumference, subcutaneous fat thickness, and the effect of fat accumulation on individuals for a more accurate assessment of body adiposity.Subsequent research has continuously introduced various obesity assessment methods, mainly including density calculation, anthropometric measurements, bioelectrical impedance analysis, dual-energy X-ray absorptiometry, computer imaging, etc.The measured indicators mainly include weight, hip circumference, waist circumference, neck circumference, skinfold thickness and more. [7]There are numerous indicators and evaluation methods for measuring obesity, each with its advantages and disadvantages, and different evaluation methods also have their unique applicability. [8]his article reviews and analyzes the existing literature, consolidating and analyzing various methods of assessing adult obesity and measured indicators.This article reviews relevant research and application advances with the goal of providing theoretical references and insights for accurate screening and diagnostic technological innovations in obesity, early intervention in obesity, and innovative theories in obesity prevention.

Methods
This narrative review was performed by collecting clinical trials, basic research, and reviews on obesity diagnostic methods.Articles published in peer-reviewed scientific journals were included.Articles were excluded if they were not written in English or published in peer-reviewed scientific journals.

Search strategy
Literature searches were performed in PubMed and Web of Science databases from the date of database inception through January 2024.The search included the following keywords: adult obesity diagnosis, adult obesity measurement, adult obesity assessment, obesity diagnosis, obesity measurement, obesity assessment, obesity diagnostic methods, obesity measurement methods, obesity assessment methods, obesity measurement index, obesity assessment index.

Study selection
We searched for relevant articles and selected articles for further reading based on the title and abstract, all included articles were carefully discussed in the present review.One thousand, one hundred twenty-eight articles were included from the initial search and 77 articles were finally selected and discussed in the review.This narrative review does not require ethical approval, because no human/patient data were used.

Density measurement method
The density measurement method treats the human body as a physical entity composed of fat and nonfat tissues.By measuring the mass and volume values of the body and substituting them into a formula, this method calculates the body density and percentage of body fat. [9]Volume measurement can be divided into the displacement method and the air displacement method.After obtaining volume data, these values are substituted into the density calculation formula to determine the percentage of body fat.The method of calculating human body density can be traced back to 1964, when Suzuki proposed the Suzuki equation for calculating human body density.In 1978, [10] Jackson improved the algorithm and subsequently introduced the Jackson-Pollock equation. [11]Both of these algorithms demonstrate high accuracy.The calculation methods for body fat percentage have developed to approximately a hundred different approaches, with some of the mainstream algorithms including the Siri equation [12] and the Brozek equation, [13] and others.The density measurement method can roughly estimate the total body fat and nonfat tissue content.However, its drawbacks include complexity in calculation, time-consuming procedures, and the inability to assess fat distribution.Additionally, for adolescent and elderly populations, the different tissue density compared to adults may lead to less accurate measurement results.
Due to its better match with the density estimation required by underwater weighing, the Siri equation is suggested to have relatively higher accuracy in situations where underwater weighing is used to determine body density.However, a drawback of the Siri equation is its relatively complex calculation process and computational challenges.Therefore, its use may be limited in scenarios such as large-scale epidemiological surveys, screening with large sample sizes, and situations where there are time constraints on detection. [14]In addition, while this calculation method works well in certain populations and contexts, it is not universally applicable to individuals of all body types and constitutions.The simplicity of the Brozek equation makes it more feasible in practical applications, which is critical for large-scale studies and epidemiological investigations.Because of its simplicity, the Brozek equation was been widely used in early studies of body fat percentage, providing convenience for the collection and comparison of large amounts of data.However, the simplified structure of this calculation method sacrifices some accuracy, especially in situations with significant individual differences and complex body types, making it less suitable for studies that require greater accuracy in body fat percentage calculation. [15]In addition, the introduction of age as a factor introduces variation in the applicability of the formula to different age groups, which could potentially affect the accuracy of the research results.

Air displacement plethysmography
Air displacement plethysmography is a method of estimating human body density based on the relationship between pressure and volume.During the measurement, the device measures the volume of air in the device chamber, subtracts the volume of air in the chamber after the person sits in it, and thus obtains the body volume value.Each measurement takes about 5 to 8 minutes. [16]This method is based on the changes in volume of the subject inside the chamber and the law of conservation of mass.It derives the body fat content by accurately measuring the air volume and the weight of the subject.This method sets the densities of lean body tissue and fat tissue as constants, approximately 1.100 g/cm³ and 0.900 g/cm³, respectively. [17]hese concepts are based on the assumption that the density of human body tissues remains constant, and are therefore somewhat idealized.In practical applications, it is possible to introduce certain correction factors or combine them with other measurement methods to improve the accuracy of the calculated results.Representative devices for air displacement plethysmography include commercially available BOD POD chambers, PEA POD chambers, and others.The use of such devices typically results in body fat percentage errors in the range of 1% to 2%, showing high repeatability compared to other measurement methods and providing relatively accurate measurement results. [18]Disadvantages include complexity of operation, high cost of equipment, and longer measurement time. [19]Some studies suggest that air displacement plethysmography can accurately estimate and control body fat within 5% of reference measurements. [20]

Underwater weighing
Underwater weighing calculates body density by measuring the difference between the body on land and the body submerged in water, thereby estimating the content of adipose and non-adipose tissues.This method was first proposed by AKERS in 1969 and was once considered the "gold standard" because of its perceived relatively high efficacy and reliability. [21]Participants are fully submerged in water while breathing through a tube connected to the outside environment.After volume and underwater weight are measured, body density and body fat percentage are calculated.Due to the higher density of human bone and muscle compared to water, individuals with greater lean mass weigh more in water, resulting in a lower body fat percentage.
Considering the presence of a certain amount of gas in human lungs, it is possible to estimate body fat percentage by assuming a model in which fat mass and fat-free mass have different densities.On the other hand, the volume of gas in the gastrointestinal tract varies from person to person (typically 100-150 mL in normal adults), and the values cannot be measured accurately.Therefore, there is a certain degree of error in the body density values obtained through by method. [22]To accurately calculate body density using hydrostatic weighing, corrections should be made to the body volume based on the volume of air in the lungs and gastrointestinal tract during the measurement.Some studies demonstrate that when based on the 4-compartment model, the standard error of body fat percentage calculated using the underwater weighing method is between 1.3% and 1.5%. [23]Nevertheless, underwater weighing remains the most classic method for estimating body composition.The principle is simple, and the error is relatively small compared to other methods of measurement.Disadvantages include higher facility and equipment requirements, longer measurement time, complicated procedures, significant influence of pulmonary and gastrointestinal gas volumes, and significant computational requirements.In addition, it is not suitable for individuals who cannot use a breathing apparatus underwater, who cannot fully submerge their bodies in water, or who cannot tolerate immersion in water.

Body mass index
BMI is an indicator based on numerical values of body weight and height that assesses overweight or obesity in individuals.The calculation involves dividing the weight by the square of the height.The World Health Organization (WHO) previously defined individuals with a BMI ≥ 30 kg/m 2 as obese and further categorized levels of obesity as follows: BMI ≥ 40.0 kg/m 2 is classified as severe obesity (class 3 obesity); BMI between 35.0 kg/ m 2 and 39.9 kg/m 2 is classified as moderate obesity (class 2 obesity); BMI between 30.0 kg/m 2 and 39.9 kg/m 2 is classified as mild obesity (class 1 obesity). [24]The International Obesity Task Force has previously proposed that a BMI ≥ 25 kg/m 2 be considered indicative of obesity. [25]Researchers, in the long-term use of this method for diagnosing obesity and screening overweight or obese patients, have found that using BMI to assess obesity has the advantages of simplicity and wide applicability.However, its disadvantage is its inability to differentiate between fat and nonfat tissue content.In addition, it cannot accurately assess for edematous patients, those with malnutrition syndrome, those with age-related muscle loss, those with low body fat, and those with higher muscle content. [26]When BMI is used to screen for obesity, it shows the characteristic of low sensitivity, and results are inconsistent when BMI is used to assess the linear relationship between obesity and various diseases. [27]The main reason that BMI cannot be used as the sole diagnostic indicator of obesity is that the standards for assessing obesity using BMI and body fat percentage are inconsistent, with body fat percentage having stricter cutoffs and BMI having looser cutoffs.However, it is undeniable that in large sample studies, BMI holds a high diagnostic value for obesity.In addition, when BMI is combined with indicators such as waist circumference, hip circumference, body fat percentage, and others, the diagnosis of obesity becomes more accurate.Moreover, and more importantly, BMI, body fat percentage, waist-to-height ratio and other indicators can effectively predict the risk of hypertension and arterial sclerosis diseases. [28]

Waist circumference
Waist circumference (WC) refers to the horizontal circumference of the waist at the level of the navel.It is the most commonly used measurement index in clinical settings to assess central obesity.It can indirectly reflect the degree and distribution of fat accumulation in the waist and abdomen of the body. [29]besity caused by abnormal accumulation of fat around the waist and abdomen is called central obesity or abdominal obesity.Excessive accumulation of fat around the waist and abdomen is closely associated with an increase in visceral fat mass.Previous research has consistently shown a strong correlation between the degree of central obesity and the risk of developing cardiovascular diseases, metabolic disorders, cancer, and other disease. [30]Therefore, the discrimination of central obesity holds greater pathological significance.The WHO advocates the use of waist-to-hip ratio and WC to assess central obesity.These 2 indicators have simple measurements and wide applicability, and hold significant importance for primary screening of obesity. [31]According to the WHO, a diagnosis of abdominal obesity is made when the WC is equal to or >102 cm for men and 88 cm for women.The International Diabetes Federation suggests that a diagnosis of abdominal obesity is established when the WC is equal to or >90 cm for men and 80 cm for women. [32]The 3 evaluation standards have significant differences, and their screening accuracy varies widely.Therefore, it is particularly important to tailor diagnostic criteria based on factors such as economic conditions, racial and gender differences, and other contextual considerations in different countries.
Measurement methods for WC include: (1) The circumference at the horizontal plane where the highest point of the iliac crest is located, as used by the National Institutes of Health in the United States, [33] (2) Suggested by the InterASIA International Collaboration on Cardiovascular Disease, the measurement is the circumference in the horizontal plane 1 centimeter above the navel, [34] (3) The circumference in the horizontal plane of the midpoint between the iliac crest and the lower edge of the rib cage at the midaxillary line, as proposed by the WHO. [35]As one of the evaluation indicators for metabolic syndrome, WC has characteristics such as easy measurement and low cost.It can effectively estimate the risk of developing cardiovascular disease and diabetes. [36]Research shows that using WC to assess central obesity is more sensitive and accurate than BMI and waist-tohip ratio. [37]Due to the neglect of the influence of height, relying solely on WC for obesity diagnosis exhibits a limitation in accuracy.This is particularly evident in special populations such as those with exceptionally tall or short stature, individuals with excessive food intake, those with high abdominal muscle content, and pregnant women. [38]

Hip circumference
Hip circumference (HC) refers to the circumference of the most prominent point of the pelvis around the buttocks.Early studies suggested using an HC >101.5 cm as an adjunct diagnostic criterion for obesity in women.If the HC exceeds 101.5 cm in women, a diagnosis of obesity can be directly made if her BMI is greater than or equal to 28 kg/m 2 . [39]In addition, some studies have shown a positive correlation between HC and the risk of polycystic ovary syndrome in women. [40]Conversely, some researchers have suggested that a larger HC can effectively reduce the risk of developing metabolic syndrome. [41]There is increasing evidence that a reduction in HC is associated with an increased risk of cardiovascular disease, coronary heart disease, diabetes and premature death in women. [42]It can be confirmed that when HC is used in conjunction with BMI as a primary screening method for obesity, the assessment of individuals with a higher content of hip skeletal muscle may be less accurate.However, due to the simplicity of measuring a single value and the relatively uniform measurement method, it is more economical and convenient compared to the measurement of other indicators.

Body adiposity index
The body adiposity index (BAI) is a method for assessing obesity based on height and HC.The specific calculation method is as follows: BAI = HC (cm)/Height (m) 1.5-18 , the BAI can effectively reflect the total body fat content.It was first proposed by Bergman et al and has been successfully applied to Mexican American and African American populations using this calculation method.The BAI can provide a comprehensive reflection of total body fat content.It was originally proposed by Bergman et al and has previously been used to assess body adiposity in Mexican American and African American populations. [43]Some studies suggest that the BAI has a significant correlation with indicators such as blood uric acid levels, blood triglyceride levels, and fasting blood glucose concentration.It also shows highly significant positive correlations with WC, BMI, waist-to-hip ratio, and other obesity assessment indices. [44]Due to the simple measurement of height and HC, this method has advantages such as simplicity and ease of use.Although the BAI is highly correlated with dual-energy X-ray scans, its value in predicting obesity is lower than WC and BMI, but higher than waist-tohip ratio. [45]In addition, some studies have confirmed that the BAI may not accurately assess the degree of obesity in individuals with body fat below 15%, and its accuracy is limited when applied to populations with extremely low or high body fat. [46]

Waist-to-hip ratio
Waist-to-hip ratio (WHR) refers to the ratio of WC to HC, and this ratio was once thought to be associated with the risk of developing cardiovascular disease in the human body. [47]The WHR, originally proposed by the WHO as an extrinsic measure to determine abdominal obesity, has significant variations in assessment standards worldwide due to differences in WC measurement methods.According to WHO guidelines, a WHR greater than or equal to 0.90 for men and greater than or equal to 0.85 for women is considered central obesity. [48]WHR, which requires the measurement of 2 values, is relatively cumbersome compared to single-site measurements.It has certain limitations in assessing central obesity, as individuals with the same WHR do not necessarily have the same amount of waist and abdominal fat. [49]WHR has a higher correlation with abnormalities in blood lipids, uric acid, blood glucose, blood pressure, and other indicators, especially in the assessment of type 2 diabetes and lipid abnormalities, where WHR accuracy is significantly higher than BMI. [50]Previous studies have confirmed a significant correlation between myocardial infarction and an elevated WHR. [51]Some studies also suggest that WHR serves as a moderate screening marker for moderate to severe obstructive sleep apnea and is an independent risk factor for obstructive sleep apnea. [52]

Waist-to-height ratio
Waist-to-height ratio (WHtR) is also known as WHtR, waistto-height ratio, and other terms.Its calculation method is as follows: WHtR = WC/Height.International standards often consider a WHtR >0.5 as a diagnostic criterion for central obesity. [53]The characteristic of WHtR is its large correlation coefficient with WC and virtually no gender differences, making it an ideal screening tool for identifying obese individuals.In addition, WHtR is also used to predict diseases such as coronary atherosclerosis, heart disease, metabolic syndrome, and adult-onset diabetes, and serves as a tool to assess the risk of developing these diseases in different individuals. [54]Previous studies have suggested that the WHtR has a better correlation with many cardiovascular and metabolic components compared to other adiposity indices.An elevated WHtR is more strongly associated with hypertension, hypercholesterolemia, and elevated low-density lipoprotein cholesterol.It demonstrates practical utility in large-scale assessments of body adiposity and effectively enhances the ability to identify cardiovascular metabolic risk. [55]Some studies also suggest that WHtR has significantly higher accuracy in predicting or screening for lipid abnormalities compared to BMI, WHR, WC, and other measures. [56]

Neck circumference
Neck circumference refers to the horizontal circumference at the narrowest point below the Adam apple.As one of the indicators of central obesity, neck circumference may indirectly reflect the subcutaneous and visceral fat content of the upper body. [57]Neck circumference is also a good predictor of the risk of type 2 diabetes, cardiovascular disease, metabolic syndrome, and is highly correlated with the risk of developing obstructive sleep apnea and hypoventilation syndrome. [58]An earlier crosssectional study of 376 participants found that neck circumference is effective in identifying excess thyroid fat in the body, thereby determining central fat content, and the accuracy is satisfactory. [59]Another cohort study of 1421 participants found a positive correlation between changes in neck circumference and visceral fat area.This suggests that using neck circumference as a diagnostic tool for abdominal obesity is practical and effective. [60]In addition, neck circumference is considered a promising tool for identifying individuals susceptible to and at high risk for cardiovascular disease. [61]Previous studies have shown that when the neck circumference is greater than or equal to 37.00 cm for men and greater than or equal to 34.00 cm for women, additional assessment of obesity is required to diagnose the presence of obesity. [62]It is worth noting that when neck circumference is used to assess obesity in different racial/ethnic groups, there are significant differences in standards.Therefore, it is advisable to implement diagnostic criteria tailored to the different ethnicities within each country.Neck circumference has several advantages in practical application, such as simplicity of measurement and high accuracy, stability and repeatability of measurement results. [63]Neck circumference can be used as an alternative indicator to BMI and WC for assessing central obesity. [64]One drawback, however, is that neck circumference standards vary widely among different ethnic groups, resulting in significant differences in criteria.

Skinfold thickness
Various instruments can be used to measure local skinfold thickness values, which can then be used to estimate body density and body fat percentage.Skinfold thickness measurement methods mainly include caliper measurement, X-ray measurement, ultrasonic measurement, etc. [65] The main measurement areas include triceps skinfold, calf skinfold, subscapular skinfold, biceps skinfold, abdomen skinfold, suprailiac skinfold, quadriceps skinfold, etc.Two to seven sites are selected each time for repeated measurements and the results are averaged. [66]Skinfold thickness methods are easy to measure, with a variety of tools available, cost effective, and suitable for large scale measurements.However, the drawback is that the accuracy of the measurements is lower compared to other methods.Factors such as the force applied by the tester when pinching the skinfold, the duration of caliper compression at the measurement site, the www.md-journal.comsubject's skin laxity, skin thickness, and the presence of edema can all affect test results.

Abdominal body shape index
The abdominal body shape index (ABSI) is an indicator of central obesity that accurately reflects the distribution of abdominal fat throughout the body. [67]The ABSI calculation method is: ABSI is highly correlated with the risk of chronic diseases such as central obesity, cardiovascular disease, and metabolic syndrome, and compared to traditional BMI, it can more accurately assess the degree of central obesity in the body.At the same time, ABSI has higher accuracy in identifying metabolic diseases such as cardiovascular disease, providing more accurate information for large-scale cardiovascular health risk assessments. [36]In addition, the ABSI calculation formula combines multiple biological parameters, taking into account factors such as abdominal fat, total weight and height, to provide a more comprehensive assessment of individual health risk.The disadvantage of ABSI is the complexity of data collection and the challenge of standardization.At the same time, the calculation of ABSI requires multiple biological parameters, including WC, BMI, and height, which can increase the complexity of data collection in practical clinical and research settings.Second, there is currently no established uniform and effective standardization system for ABSI.Different studies and clinical practices may use different calculation methods and standards, thereby reducing the consistency of comparison and application.Further research is needed to validate the applicability of the ABSI in different populations and to explore its predictive accuracy for health status in different populations.On the other hand, the combination of ABSI with biological markers such as inflammatory indicators and metabolites to enhance its comprehensiveness in multifactorial risk assessment is also one of the future research hotspots.Overall, the ABSI shows potential value in assessing central obesity and chronic disease risk, but its application requires further research and standardization.In the future, with a deeper understanding of the impact of central obesity and technological advances, the ABSI may become a more accurate and comprehensive tool for health assessment.

Bioelectrical impedance analysis
Bioelectrical impedance analysis (BIA) is a method that utilizes the different conductivity coefficients of adipose tissue and other tissues in the body.It calculates body impedance and then calculates body fat percentage based on the regression equation between body fat content and body impedance.Commonly used devices include two-electrode, four-electrode, six-electrode, and eight-electrode devices. [68]The accuracy of BIA depends on factors such as humidity and tightness of contact between the subject and the electrodes, room temperature, the subject's skin temperature of, the subject's hydration level, the precision of the testing device, and the algorithm used. [69]Body fat percentage, is the ratio of body fat mass to total body mass, which directly reflects the body fat content and ratio.Previous studies have proposed criteria for diagnosing obesity: a body fat percentage greater than or equal to 25% for men and greater than or equal to 35% for women. [70]Subsequent studies have found that normal-weight individuals may have abnormal body fat content, especially in the case of normal-weight obesity.In this population, individuals are of normal weight but have a significant proportion of fat in their body composition.It is challenging to identify this group using external measurements such as BMI, WC, and HC.Therefore, using BIA to analyze body fat percentage becomes particularly important.BIA can comprehensively calculate the content of skeletal muscle and adipose tissue in the body, and the stability of measurements is relatively high within the same population at different times.However, its limitations include the influence of various factors on the measurement results, its unsuitability for measuring local fat content, and its applicability to epidemiologic surveys in different populations. [71]In addition, due to the large number of impedance equations, it remains to be verified whether different calculation methods are applicable to populations in different countries.

Dual-energy X-ray absorptiometry
Dual-energy X-ray absorptiometry (DEXA) is a procedure that uses X-rays to measure bone density and tissue composition.This technique involves directing X-rays into the human body and analyzing the absorption characteristics of different tissues.It measures and analyzes the amount of bone, fat, and lean tissue in the body. [72]DEXA can accurately assess body fat content and distribution, which is critical for evaluating central obesity and fat distribution in different regions of the body.DEXA collects X-ray absorption data from bones and tissues, producing high-resolution images that allow precise measurement of fat and lean body tissue at both the global and local levels.This precision gives DEXA a unique advantage in diagnosing obesity and providing insight into fat distribution patterns.Overall, DEXA has an extremely high correlation with computed tomography measurements, good repeatability, and excellent accuracy. [73]espite the high-precision advantages of DEXA, the issue of radiation exposure must be considered in practical applications.Therefore, when using DEXA, it is important to balance its benefits and risks.In addition, the disadvantages of DEXA include higher test costs compared to other methods, insufficient precision in assessing waist and abdominal fat content, and susceptibility to factors such as gender and age. [74]

Computer imaging method
Computer imaging methods mainly include magnetic resonance imaging (MRI) and computed tomography (CT).Both MRI and CT can accurately differentiate and measure visceral or subcutaneous fat, making them the gold standard for determining and measuring obesity.The advantage of CT is its extremely high accuracy and minimal factors that can affect the measurement results.However, this method is associated with longer measurement times, higher costs, and high equipment dependency. [75]In addition, CT involves radiation and is therefore rarely used for obesity screening.Improving imaging quality while effectively reducing radiation dose is also one of the focus areas for future research.Compared to CT, MRI can noninvasively measure human spatial information and tissue structure.The advent of MRI has addressed the long-standing limitation of CT in capturing anatomical information within the body.MRI has a wide range of applications, but it has long acquisition times, high acquisition costs, and is not suitable for patients with metal implants. [76]

Limitations
There are some limitations to our research.First, this study did not include all relevant literature, and there may be missing reports of obesity diagnostic methods that are not included in the literature database or not widely reported.On the other hand, various obesity diagnostic methods that have been reported are proposed for different regions or ethnicities, which may limit the comparability of research results.In addition, the accuracy of various obesity diagnostic methods can be easily influenced by nonstandard measuring tools, nonstandard measuring postures, measuring environments, and nonstandard measuring operations, which may lead to biased research results.Therefore, the authors believe that more high-quality research on obesity diagnostic methods is needed.

Conclusion
There are numerous indicators and methods for measuring obesity, each with its own advantages and disadvantages.Different assessment methods also have unique applicability.When assessing obesity, differences in body composition due to factors such as gender, age, race and ethnicity should not be overlooked.In practice, selection should be based on actual conditions.The combination of multiple measures, the use of double standards, and the adoption of multi-criteria screening strategies are critical to increasing the accuracy of obesity assessment.With the development of biomedical, BIA with its safety, speed and accuracy shows promising potential in screening and assessment of obesity, demonstrating broad application prospects.